The present invention relates to the field of wavelength division multiplexing optical networks with packet granularity capability and coherent detection and more particularly to the chromatic dispersion compensation in such networks.
A wavelength division multiplexing optical network refers to a network comprising a plurality of nodes connected by optical links wherein data signals are transmitted through a plurality of channels having different wavelengths and which are multiplexed to be transmitted through the optical links of the network.
Packet granularity or packet switching granularity refers to the possibility to add or drop one or several optical packets of a signal in an intermediary node while transmitting the other packets transparently. In such networks, the packets are usually transmitted within time slots so that the packets of the different channels are synchronized.
Equipments with packet granularity capability are more and more implemented in the optical communication network in order to enhance the flexibility of communication networks. Such equipments are referred to as packet optical add-drop multiplexers (POADMs). However, a POADM requires compensating for the chromatic dispersion induced by the transmission of optical packets through links of the network.
Indeed, one aspect of the chromatic dispersion called inter-channel chromatic dispersion refers to the fact that packets transmitted in channels of different wavelengths experience different travelling speeds so that time shifts or time offsets are introduced between packets emitted simultaneously. Need is then to resynchronize the packets to enable their processing at the receiver.
Besides, another aspect of the chromatic dispersion called intra-channel chromatic dispersion refers to the distortion undergone by the signal representing the bit coding of a packet during its transmission through the links of the network, rendering the bit decoding difficult and possibly erroneous.
One way to compensate for both aspects of the chromatic dispersion is to use in-line compensators located along the links of the network. However, in-line components introduce additional losses that need to be compensated by additional amplifiers. Moreover, such amplifiers introduce additional costs and generate additional noise so that the distance that can be reached transparently with a given quality of signal may be reduced.